Aerosolizing formulations for inhalation has been considered as a convenient alternative to injection for decades. This alternative to injections is particularly interesting for drugs which cannot be delivered orally, e.g. insulin. Although most compounds will effectively move from the lungs into the circulatory system there is considerable unpredictability in how much aerosolized formulation reaches the areas of the lungs where the material can move into the circulatory system. This results in inefficiency and unpredictability of dosing. A number of devices have been proposed for improving the efficiency of aerosol delivery, monitoring patients and teaching patients to correctly use delivery devices.
There are several different types of devices which use generally different mechanisms and methodologies to produce aerosols for inhalation. The most commonly used device is a metered dose inhaler (MDI) which comprises a drug formulation container with the formulation including a low boiling point propellant. The formulation is held in the container under pressure and a metered dose of formulation is released as an aerosol when the valve on the container is opened. The low boiling point propellant quickly evaporates or “flashes” when the formulation is exposed to atmospheric pressure outside the container. The particles of formulation containing the drug without the propellant are inhaled into the patient's lungs and thereafter migrate into the patient's circulatory system. There are a number of different types of MDI devices. Devices of this type are disclosed in U.S. Pat. Nos. 5,404,871 issued Apr. 11, 1995 and U.S. Pat. No. 5,364,838 issued Nov. 15, 1994.
Another type of device is the dry powder inhaler (DPI) device. As indicated by the name such devices use formulations of dry powder which powder is blown into an aerosolized cloud via a burst of gas. Typical DPI devices are shown in U.S. Pat. No. 5,775,320 issued Jul. 7, 1998 and U.S. Pat. No. 5,740,794 issued Apr. 21, 1998.
Yet another type of aerosol delivery device forces a formulation through a porous membrane. Formulation moving through the pores breaks up to form small particles which are inhaled by the patient. Devices of this type are shown in U.S. Pat. No. 5,554,646 issued Aug. 13, 1996 and U.S. Pat. No. 5,522,385 issued Jun. 4, 1996.
Each of these devices has some advantages and disadvantages. The object of each is substantially the same—to repeatedly produce a fine mist aerosol wherein the particles are substantially uniform in size and within a size range of about 1 micron to about 5 microns. A patient can be accurately dosed if the device can repeatedly start with a given amount of formula and produce a known amount of aerosol with particles having sizes within a known range. The present invention endeavors to provide a device and method for obtaining accurate repeatable dosing of a patient with an aerosol.